The prognosis for pancreatic cancer (PC) patients is dismal, with a 5-year survival rate of less than 6%. This is in part due to the propensity of PC to metastasize prior to disease detection and the resistance to cytotoxic therapies. A significant portion of therapeutic resistance in pancreatic cancers comes from the support of a unique tumor microenvironment. This tumor microenvironment includes significant numbers of infiltrating myeloid cells including tumor-associated macrophages, which exacerbate responses to therapy by inducing immunosuppression. Thus, where clinically feasible reprogramming the immune microenvironment would improve responses to cytotoxic therapy even in resistant tumors. One unique approach to this problem is to target the C-C chemokine receptor type 2 (CCR2). Signaling through C-C chemokine receptor type 2 (CCR2) is critical to the mobilization of IM and their recruitment to inflamed tissue. Our preliminary and published findings clearly show that blockade of IM mobilization using a novel CCR2 inhibitor, PF-04136309 slows tumor progression and prevents metastasis in mouse models of PC. Thus, selective targeting of inflammatory monocytes holds significant promise for the treatment of PC. Based on this exciting and provocative preliminary data, we have initiated a Phase Ib clinical trial targeting th CCR2 signaling pathway in patients with locally-advanced pancreas cancer. While targeting CCR2 holds strong clinical potential for bolstering cytotoxic therapy it may be even more promising in combination with immunotherapy. Strikingly, our studies have found that CCR2 blockade overcomes immune suppression to re-initiates anti- tumor responses by CD8+ CTLs. However, CCR2 inhibition also leads to up-regulation T cell checkpoint pathways such as Programmed Cell Death 1 (PD1) ligands and Cytotoxic T-Lymphocyte Antigen 4 (CTLA4). These data suggest that the combination of CCR2 inhibition and anti-CTLA4 and/or PD1 based immunotherapy would be highly effective at generating the type of durable anti-tumor immune responses necessary to impact patient survival. Thus, building on our published work, new preliminary data, and samples from our existing clinical trial this grant will focus on understanding and exploiting the mechanisms by which CCR2 blockade reprograms the pancreatic tumor microenvironment to bolster anti-tumor immunity. Our overall hypothesis is that blockade of CCR2 signaling reprograms the tumor microenvironment to improve responses to immunotherapy. To test this, we will: 1) Determine the optimum therapeutic regimen for targeting CCR2 to improve immunotherapy. 2) Determine the effect of CCR2 blockade on T lymphocyte responses in human pancreatic cancer Summary: The proposed research will assess the efficacy of targeting CCR2 to improve immunotherapy, thus allowing this strategy to be integrated into future clinical trials. At the same time our studies will improve our understanding of the mechanism(s) by which CCR2 blockade improves CTL responses in humans and mice.